Optics and refraction for mbbs in a simplified view

1. Optics and Refraction
Dr GOPI KRISHNA
MBBS,MS OPHTHALMOLOGY
FELLOW IN PHACOEMULSIFICATION AND SICS ( ANTERIOR SEGMENT)

4. Physiological optics

8. Geometrical optics
• Behaviour of light rays is determined by ray optics
• Where ray of light follows path of straight line
*
• Rectilinear propagation
• Reflection
• Refraction

9. Reflection
• Change in path of rays with out change in medium.

10. Mirrors
Plane mirror – looking mirror,one side is silvered and other side is
polished .
Images formed by plane mirrors – size same as object,laterally
inverted,virtual in nature,same distance
Spherical mirrors : concave and convex

11. • A convex mirror is also known as a diverging mirror as this mirror
diverges light rays when they strike its reflecting surface.
• Virtual, erect, and diminished images are always formed with convex
mirrors, irrespective of the distance between the object and the
mirror.
• By changing the position of the object from the concave mirror,
types of images can be formed.
•

12. Lateral inversion in plane
mirror

14. Virtual erect and diminished

16. Refraction

17. • Incident ,refracted are on opposite sides of normal ,but all are in
da,same plane.
• Refractive index

18. Total internal reflection
• When a light enters from denser medium to rare medium is incident
at an angle greater than critical angle ,then the ray gets reflected back
in to the denser medium .
• Critical angle: angle of incidence in the denser medium corresponding
to which angle of refraction is 90 degree in rare medium
Uses: applantion tonometer,gonioscopes,fibre optics.

20. Prisms

21. Uses of prisms
• In gonoiscopes,aplantation tonometer,keratometry
• Relieve diplopia
• To examine angle of deviation (squint)

23. Lens
• Transparent refracting medium.
1 spherical
A) convex B) concave
2. Cylindrical lens

24. Cardinal points of lens
1. centre of curvature( C ): centre of sphere of which refractive lens is
the part.
2. Radius of curvature ®: radius of sphere
3. Principal axis (AB) : line joining the centre of curvatures of its
surfaces.
4. Optical centre (O): nodal point,point on principal axis passing where
rays do not undergo any deviation
5. Principal focus (F):point on principal axis where parallel rays after
passing through the lens either converge or appear to diverge
6. Focal length (f): distance between optical centre (O) & principal
focus( F).
7. Power : ability to converge or diverge the light (p=1/f)

25. • Principal focus (F)
• Optical centre( O)
• Nodal point (N)
• Principal axis AB
• Power
• Focal length (f)
• Centre of curvature (C) Cardinal points of convex lens

29. Spherical lens
1 .Convex :
• thick at centre and thin periphery,
• Object close to lens appears magnified
• When lens is moved object appears movement in opposite direction
• Uses: hypermetropic correction,aphakia,presbyopia
2 .Concave :
• Thin at centre ,thick at periphery
• Object through it appears minified
• Movement with lens is in the same direction
• Uses: myopic correction

30. Cylindrical
• Lens acts only in one axis
• Convex and concave
• Uses : astigmatism correction ,Maddox rods,

33. Schematic and reduced eye

45. Thank you